This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of this project is to synthesize and characterize PSMA-targeted nano-conjugates;evaluate in vivo behavior of the nanoconjugates in normal and prostate tumor bearing mice;and apply the nanoconjugates to noninvasive MRI/PET imaging of prostate cancer. In the United States, prostate cancer (PCa) has been consistently the second leading cause of cancer-related deaths of men. Currently the American Cancer Society recommends annual checkups with the prostate-specific antige test and the digital rectal examination for the early detection of PCa in men at certain ages based on their ethnic groups and family history. Although the routine PSA-based screening has been introduced to the diagnosis of PCa over two decades and has become probably the most common clinical test of cancer, it is still in debate about the benefit of the PSA screening and the upper limit of normal PSA values. On the other hand, the PCa biopsies routinely performed with transrectal ultrasound cannot warrant a definitive stage of PCa because PCa can be isoechoic and indistinguishable from the surrounding tissues. Therefore it is of great significance to develop new techniques for the non-invasive detection of PCa with high sensitivity and specificity. Among the non-invasive imaging modalities, computed tomography (CT) has been traditionally used to evaluate the extent of local PCa, more recently magnetic resonance imaging (MRI) has also joined the clinical practices for more accurate staging of PCa as the MRI techniques rapidly evolve. Because CT and MRI are typically anatomical imaging techniques, they are inherently short of sensitivity as compared to the functional/metabolic imaging modalities, such as positron emission tomography (PET). However, the most commonly used PET radiopharmaceutical, 18F-FDG, is not quite successful at identifying PCa (until PCa becomes metastatic) as it is in the detection of other tumors because of the low glycolytic rate of PCa and high background due to the normal excretion of 18F-FDG through urine. To date, the role of PET in prostate cancer has not been established. The goal of this proposal is to explore a new approach that will combine the advantages of MRI and PET for the diagnostic imaging and staging of PCa. We propose to dope positron-emitting isotopes to superparamagnetic iron oxide nanoparticle to make nanosized dual MRI/PET probes for the detection of PCa by multi-modality (anatomical MRI plus functional PET) molecular imaging approaches, so that the sensitivity and specificity of PCa diagnosis could be significantly improved. In this proposal, we choose arsenic-74 due to its low endpoint positron energy (0.94 MeV) that provides higher spatial resolution of PET, and its relatively long half-life (17.77 days) that allows us to carry out the procedures of making the dual-modality imaging probes. In perspective, the long half-life also allows global delivery of such imaging probes. Two prostate specific membrane antigen (PSMA) targeting molecules (a new PSMA monoclonal antibody and a novel PSMA-targeting RNA aptamer) will be used to construct the PSMA-targeted nano-conjugates. Three animal models (intra-femoral, subcutaneous, and orthotopic) using two prostate cancer cell lines, C4-2 and PC-3 cells, will be used for the imaging probe evaluations in this proposal, because C4-2 is an androgen responsive cell expressing PSMA and PC-3 is PSMA-devoid AIPCa cell that will serve as negative control. Two specific objectives are arranged in this project: Objective I. Preparation/characterization of 77/74As-doped iron oxide nanoparticles and construction of PSMA-targeted nano-conjugates;and Objective II. Evaluation of the PSMA-targeted nano-conjugates in PCa xenograft mouse models via the conventional biodistribution and small animal MRI and PET imaging methods. In Objective I, we will establish protocols to prepare dextran-coated 77/74As-doped iron oxide nanoparticles and PSMA-targeted nano-conjugates. We plan to make four PSMA-targeted nano-conjugates by covalently attaching the two targeting molecules to the dextran-coated 77/74As-doped iron oxide nanoparticles with sizes of 25 nm and 35 nm, for the studies in the Objective II. The in vitro stability will be determined by incubating the nano-conjugates with fresh rat serum over 48 h and follow-up radio-HPLC analysis. The tumor-targeting property of the nano-conjugates will be evaluated in C4-2 and PC-3 xenograft models (subcutaneously in the flank) by the conventional biodistribution method. The nano-conjugates that show optimal behavior in vitro and in vivo and tumor-targeting property will be further evaluated by small animal MRI and PET imaging in two C4-2 xenograft models (orthotopic and intra-femoral) for the detection of localized and metastatic tumors. Both biodistribution and small animal imaging results will be compared with the respective PSA data. We anticipate the PSMA-targeted nano-conjugates will be able to serve as dual-modality imaging probes and provide higher sensitivity and specificity for PCa detection than either of the single-modality imaging approaches and the PSA test.